This invention pertains to rotary mowers, primarily for grass cutting and lawn maintenance where the grass clippings are re-cut or mulched by a high speed rotating blade inside of a housing or a deck that must be kept reasonably clear of grass build-up on the underside for efficient cutting.
Mowers have been proposed with scrapers that rotate on the same shaft as the cutting blade underneath the housing for keeping the grass cleaned off. For example, U.S. Pat. No. 3,396,518 issued Aug. 13, 1968 shows a scraper revolving by friction on an eccentric bearing about the motor shaft. However the scraper is not positively driven, and the underside of the housing must be flat. Grass build-up overpowers the scraper, so a hole is provided to manually free it up. Power rotating the scraper would be impractical. Its eccentric motion would unbalance the mower causing excessive vibration. Also, its rotary inertia would be too high for conventional blade stopping or braking systems. The stopping requirements of safety regulations, e.g., the American National Standards Institute (ANSI) for outdoor power equipment require stopping a blade from full rotation within a few seconds from maximum rpm for residential use. For a high inertia blade this becomes difficult for the available braking mechanisms on such mowers, ruling out any possibility of putting a self-cleaning device with high inertial mass on existing mowers.
Another attempt to solve the build up problem is disclosed in U.S. Pat. No. 4,450,673 issued May 29, 1984. There a counter rotating housing driven by belts rotates in an opposite direction to the main blade, and it also carries auxiliary blades for re-cutting the grass clippings, with the object of keeping the underside reasonably free of build-up. This arrangement suffers from more difficulties than the rotating scraper design described above. A spinning mass as large as the counter rotating housing in this disclosure would simply overwhelm a conventional braking systems making it impossible to comply with ANSI standards.
Another attempt to solve the build-up problem is shown in U.S. Pat. No. 5,042,242 issued Aug. 27, 1991. Here a hub rotates with the blade and has a radial flange above the blade. The flange has opposed lugs from which pivot lengths of chain. Theses are supposed to act as blowers when the grass is dry to help keep the underneath of the housing clear. In wet grass, the chains are replaced with blades sharpened in the direction of rotation. Wet grass is re-cut to a finer state for supposedly to help prevent build-up, however, whether chains or blades, they are not self-supporting, and would drop or hinge from the flange when the blade rotation stops. Also, they would get tangled in the blade when starting. Both must be balanced to prevent vibration and noise. The rotating masses of the chains or blades would be too much for existing braking systems, and could not be deployed on existing mowers. Power consumption also would be a problem. The horse power of existing mowers would be over taxed driving the main cutting blade and these rotating masses too. Thus, these devices if sold for use with existing mowers would be impractical. Not only would the mower have trouble starting, but at operating speed the power drained off by the excess mass would cause the engine to lug down in heavy grass or vegetation.
Still another patent (U.S. Pat. No. 5,483,790 issued Jan. 16, 1996) discloses a revolving disk and mulching blade in a torsional air flow chamber where curved baffles or a double walled inner housing are situated to deflect the clippings back into the blade for re-cutting before discharge from the rear of a deck. This arrangement is not cost effective, and is also flawed as a self-cleaning system since the grass buildup is not prevented in the most sever regions, near the outer periphery of the housing, and efficient removal is limited to the inner circumference of the torsional air chamber. Moreover, the high speed rotating disk only adds more mass to the motor shaft making it difficult to stop within the ANSI standards.
My present invention goes in a different direction than the prior art in solving the grass build-up problem.
My prior patent application, Ser. No. 07/679,567, filed Apr. 2, 1991, now abandoned, is incorporated herein as if set forth in full, and discloses low mass, linear elements that rotate above the motor driven blade near the underside of the housing. The low mass elements generate air pulses of a high frequency proportional to the rpms of the rotating shaft that beats and disperses the grass clippings into a finer state than as cut by blade. They are re-circulated or mulched further by the blade, and conveyed either into a discharge chute or distributed on the ground. The combination of physical attack and high frequency air pulses largely prevents the grass particles from adhering to the underside of the housing. The elements have enhanced aerodynamic power due to the close proximity to the housing, but also where obstructions, such as bolts or curved baffles exist inside the housing, the high velocity air pulses, and eddies, impact against theses obstructions too, or any other irregular surfaces, to maintain the housing relatively clean. The cleaning action is especially powerful toward the periphery of the elements where the angular velocities are greatest. The air borne particles are aerodynamically pulsed the more violently within the housing at the place where accumulations tend to be greatest. The underside of the housing together with the high velocity elements tend to form an upper chamber where the clippings are beat into fine particles more easily conveyed out by the turbulent pressure head created by the blade out of the housing.
This upper chamber of high velocity pulses is complemented by a lower chamber defined between the mower blade and the elements creating a recirculating air flow. In this chamber the rotating tips of the blade and the linear elements produce air turbulence of a recirculating, toroidal pattern. Blade geometry in mulching mowers produces violent updrafts, particularly at the tips, where a high pressure head exists while nearer the shaft, at lower angular velocities, a lower pressure head exists forcing the grass particles to move in a toroidal circular pattern. The flexible, linear elements extend as far as the tips of the blade to augment the recirculation and cutting action.
Moreover, the turbulent air flow pattern in the lower chamber is increased in part due to the elements cooperating with the blade, and the lower drag from having very little accumulation of grass cuttings under the housing, all of which helps create a uniform discharge at higher pressure head. The finely divided grass particles are conveyed as a fluidized stream so dispersed as to reduce wind rowing or where an attachment for collection or bagging is being used, to facilitate this operation.
Where the self-cleaning system of the invention is employed with multiple blade mowers, the linear elements cooperate with each blade, and the interior housing surfaces to cause turbulent flow of the grass particles into a discharge opening, or where bagging, to force feed the bag.
In one embodiment, the low mass, flexible string elements are spring steel, like music wire. Others are polymer string filaments. Nylon strings may have an abrasive imbedded in them for greater life. Other elements may be durable, flexible plastic linear members with a metal cutting edge sharpened in the direction of rotation for durability. Or they may be aerodynamically shaped in cross section to produce more up draft, if convex on the upper side, or down draft, if the shape is reversed to minimize power consumption. Where the elements are flexible filaments, or more stiff linear elements that hinge at their base, the centrifugal force causes them to become essentially rigid.
An important difference of the invention and prior art systems is that the rotating mass of my self-cleaning system is slight as compared to the rotating mass of the blade. The mower is easier to start, and during operation, the mass of the elements is insignificant in terms of the inertia of the entire rotating mass. Where one linear element is employed, it is too light to unbalance the mower shaft, or cause objectionable noise and vibration, and where they are employed in opposed pairs, the natural balance is not upset by wear or breaking away of a single element.
Another important difference is the self-supporting feature of the flexible elements. Where the base is secured to a rotating hub, the radius of the hub is approximately half that of the blade leaving a shorter radial length for the elements than heretofore has been employed so the flexible material is self-supported, and doesn""t drag or drop into the blade when stopped. Where the elements are rigid members attached to the hub, hinging at the base is prevented by a mechanical engagement with the hub but easily disconnected if needed to replace an element.
The flexible elements extend radially out from a hub or carrier. In one embodiment this is a disk rotating above the blade. In another it is a base with opposed tapered wings angled upwardly near the underside of the housing. In any case, the carrier is symmetrical with the rotating axis and positions the elements in a plane near the underside of the housing. The base holds the inner ends of the flexible elements fixed firmly against the pulling action of the centrifugal force. For the self-supporting elements the centrifugal force has little effect in extending them out to full extension since the tips are already self supported spaced above the tips of the blade, i.e., the tips are at the same radial distance from the axis of rotation as the ends of the blade. The housing has a relatively flat undersurface which defines, with the base and rotating elements, an annular upper chamber. This chamber, due to the high position of the elements on the shaft, is narrow, preferably not more than about a half inch wide. The low mass inertia of the elements relative to the blade makes it unnecessary to perform balancing operations, and the need to replace an element that is broken is usually evident only by periodic inspection.
In one embodiment, an assembly with a lower wall is provided in which a hole is centrally located for mounting it on the blade shaft and having an upper portion to which the linear elements are adapted to mount, the assembly being sold as a self-cleaning retro-fit package for existing mowers that were not designed for self-cleaning as manufactured. The elements are housed entirely by the mower deck and cannot cause injury or damage. The existing braking systems for stopping blade rotation within ANSI standards will still be effective with my self-cleaning retro-fit package since no appreciable rotating mass is added.
A primary object is to provide a low mass, linear element spaced above the mower blade and near the undersurface of the housing of a length from its anchor on the inner end to its outer tip that is proportional to the blade radius adapted to rotate at blade speed to create high velocity air pulses in a chamber defined by the rotating element above the blade and below the housing.
Another object is to provide a self-cleaning retro-fit package that is adapted to be assembled with an existing rotary mower without violating ANSI standards for safety in blade stopping requirements.
The self-supporting feature allows use with blades up to 24 inches in diameter without the elements hinging or dangling down into the blade when stopped or getting tangled on start up.
The flexible, light weight nature of the design improves the economy of manufacture, minimizes any damage to components or due to overloading, and reduces impact forces to the elements or mower itself in operation.
If the conditions are such that build-up occurs in the operating area of the elements, or they become worn from excessive use, mowing can continue with the conventional mulching not being interfered with.
Another object is to provide a self-cleaning mower that discharges more uniformly or when bagging the grass clippings, a turbulent pressure head is created to forcefully discharge clippings into a bagging system while keeping the underside of the deck relatively clean. Advantageously, this is achieved under substantially any foreseeable operating conditions of the grass, wet or dry.
These and other objects of the invention will become more apparent by referring to the following detailed description of a preferred embodiment of the invention.